In our earlier granted patent, U.S. Pat. No. 6,850,183, we describe a slope monitoring system based on interferometric radar measurements. The radar employs a mechanically scanned dish antenna to achieve azimuth and elevation coverage. The radar described in our earlier patent used a 0.92 m diameter parabolic dish mounted on a sturdy tripod and controlled by separate motors and gears for azimuth and elevation movement.
It has been found that the mechanical scanned dish antenna is a source of mechanical instability so an alternate system is required. Furthermore, the mechanical scanning equipment has a large power requirement that is provided by a generator, thus increasing the size and cost of the radar. There are practical limits on the size of a mechanically scanned dish for slope monitoring applications so for long range applications or higher resolution applications an alternative is needed.
Synthetic aperture imaging with circular and elliptical boundary arrays has been analysed for acoustic applications by Kozick [Coarray Synthesis with Circular and Elliptical Boundary Arrays; IEEE Trans. Image Processing; Vol 1 No 3 Jul. 1992] and Norton [Synthetic Aperture Imaging with Arrays of Arbitrary Shape—Part II: The Annular Array; IEEE Trans. Ultrasonics, Ferroelectrics and Frequency Control; Vol 49 No 4 April 2002]. Kozick and Norton both reference Norton's earlier paper [Acoustic Holography with an Annular Aperture; J. Acoustic. Soc. Am. Vol 71 No 5 May 1982]. Reference may also be had to a early paper by Milder & Wells [Acoustic Holography with Crossed Linear Arrays; IBM J. Res. Develop. September 1970] which describes the advantages of orthogonal linear arrays of receiver and transmitter elements.
Although not directly applicable to the radar situation the theoretical analysis in these papers provides a useful background for considering a perimeter array as an alternative to the dish antenna.